Method of making one-piece multifocal lens blanks

ABSTRACT

The method of manufacturing a multifocal lens blank which may finally be processed into a prescription lens having reading and distance portions separated by a shoulder extending the width of the lens, wherein a plurality of optical glass workpieces, specially shaped for efficient further processing, are blocked about the circumferential edge of a blocking wheel and auxiliary slabs of optical glass are provided in the spaces between adjacent pieces. During the grinding and polishing operations, which are performed on the workpieces to transform them to lens blanks, the auxiliary slabs provide the additional support needed by the processing tools to form relatively undistorted lens surfaces.

United States Patent Primary Examiner-Lester M. Swingle Attorneyl(ane,Dalsimer, Kane, Sullivan & Kurucz ABSTRACT: The method of manufacturinga multifocal lens blank which may finally be processed into aprescription lens having reading and distance portions separated by ashoulder extending the width of the lens, wherein a plurality of opticalglass workpieces, specially shaped for efficient further processing, areblocked about the circumferential edge of a blocking wheel and auxiliaryslabs of optical glass are provided in the spaces between adjacentpieces. During the grinding and polishing operations, which areperformed on the workpieces to transform them to lens blanks, theauxiliary slabs provide the additional support needed by the processingtools to form relatively undistorted lens surfaces.

PATENTEU MAY 4 I97! SHEET 2 OF 4 lNVENTOR W/auAM A4v cw 7790/11 7%;ATTORNEYS PATENTEDMAY 4:971 3,577,690

SHEET 3 OF 4 INVENTOR W/CL/4M /t4 C4 20 ATTORN EYS PATENTEU HAY 41911(577,690

sum 0F 4 INVENTOR 140.4404 M. c/meam/ ATTO RNEYS METHOD OF MAKINGONE-PIECE MULTIFOCAL LENS BLANKS CROSS REFERENCE TO RELATED APPLICATIONThis application is a division of my application Ser. No. 688,454, filedDec. 6, 1967.

BACKGROUND OF THE INVENTION Heretofore, the typical blank used in theoptical industry for the manufacture of one-piece, multifocal lenses ofthe type having a reading portion and distance portion formed on thefront surface and a separating ledge or shoulder at each field of visionjuncture has been confined to a substantially square or rectangularshape. The typical prior art process for preparing such lens blanks isdisclosed in US. Pat. No. 3,066,458 and the prior art blank is depictedin FIG. 2 of said patent.

The reason for the particular shape of the prior art blank is thatduring the preparation of the blanks, the workpieces from which theblanks are produced are mounted about the circumferential periphery of ablocking wheel which is rotated while grinding and polishing operationsare performed to form the semifinished blanks. The performance of thesegrinding and polishing operations requires that the abrading surface ofthe processing tool be brought to bear on the rotating blanks in orderto impart thereto the desired radii of curvature. The processing tool isbiased toward the center of the blocking wheel and the grinding surfacerests upon the workpieces. If there is substantial space betweenadjacent workpieces, either the tool would slip or fall into the space,thereby preventing further grinding or polishing, or an aberratedsurface would result from the varying unit pressures exerted by thegrinding or polishing tool as the pattern of glass area under the toolchanged with the rotation of the blocking wheel. In order to minimizeany spacing or gaps between adjacent workpieces, the prior art requiredthe use of a straight-sided square or rectangular workpiece which couldbe closely abutted against the workpiece adjacent it. Suitableadditional slabs were required to fill the gaps between workpieces inthose usual instances when the diameter of the blocking wheel and thewidth of the workpiece were not such as to permit complete encirclementof the blocking wheel circumferential edge by a whole number of pieces.Round or semiround workpieces could not be used in accordance with priorart teachings since they would tend to produce too great a gap in thecusp formed between adjacent pieces.

The square or rectangular semifinished blank in accordance with theprior art teachings presents many difficulties to the prescriptionlaboratory which must ultimately produce the lens by processing theunderside of the semifinished blank according to some desiredprescription. The principal difficulty is based on the fact that theoptical and geometric center of the rectangular blanks don not coincideand hence when the blank is blocked on the optical center, there isanuneven distribution of glass about the blank. This uneven glassdistribution causes pressure variations to occur during the grinding andpolishing of the under side of the blank which, in turn, may result inthe optical center drifting from its prescribed Iocation. Also, duringthe under side processing of the rectangular blank, those portions whichextend far out from the block are ground to a substantial knife edgeresulting in a lens which is both hazardous and extremely fragile andsubject to breakage.

To overcome the above described difficulties, the prescriptionlaboratory must in some manner preform the edge of the blank before itis processed. This is generally done by cribbing or breaking off theextra portions of glass that extend far beyond the lens block. Thisoperation is both time consuming and costly and also produces a blankwith dangerously jagged edges.

SUMMARY OF THE INVENTION It is, therefore, the primary object of thepresent invention to provide an improved method for producing multifocallens configuration about the circumferential edge of a blocking wheel ina suitable manner. Similarly, auxiliary slabs of optical glass havingsubstantially the same thickness and front and underside radii ofcurvature as the workpieces, and having a configuration which is such asto fill the space between adjacent workpieces, are secured to the wheelin the spaces between adjacent workpieces. Grinding and polishingoperations are then carried on to produce semifinished lens blanks. Whenthe processing is completed, the blanks and slabs are removed from thewheel and the slabs are discarded. The lens blank so produced and havingthe desired nonrectangular configuration is then forwarded to theprescription laboratory to undergo further processing in accordance withany particular prescription.

As an alternative method of producing the nonrectangular blanks, theauxiliary slab may be initially bonded to a workpiece and thereafter thecombined piece and slab are secured to the blocking wheel in a standardmanner. After grinding and polishing, the bonding material may beremoved, separating the blank and slab, and the slab may be discarded,leaving the lens blank ready for delivery to the prescription lab. Inthis case the configuration of the slab would have to be such as tocomplement that of the preferred blank shape so as to permit a combinedworkpiece and slab to substantially abut against a similarly combinedworkpiece and slab unit when both are mounted on a blocking wheel. Thedimension of the slab should also be chosen so as to allow theperipheral edge of the wheel to be covered by a whole number of unitswithout requiring the use of an odd-shaped end piece between the lastand first units.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. I is a perspective view of a fully loaded prior blocking wheel forproducing multifocal lens blanks;

FIG. 2 is a perspective view of a prior art lens blank depicting apreferred partly round configuration in phantom;

FIG. 3 is a perspective view of an unfinished partly round blank whichcan be produced therewith is shown in phantom;

FIG. 4 is a perspective view of a triangular auxiliary slab which may beutilized in accordance with the present invention;

FIG. 5 is a top plan view of a suitable partly rounded blank;

FIG. 6 is a side elevational view of the blank of FIG. 5;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 5;

FIG. 8 is a perspective view of a blocking wheel upon which a pluralityof lens blanks are being ground in accordance with the present inventiondepicting the relative positions of the workpieces and auxiliary slabs;

FIG. 9 is a developed view of the peripheral surface of the lensblocking wheel of FIG. 8;

FIG. 10 is a sectional view taken along line 10-10 of FIG. 9;

FIG. 11 is a sectional view taken along line 111 1 of FIG. 9;

FIG. 12 is a sectional view taken along line 12-12 of FIG. 9 depictingthe grinding and polishing wheel in phantom;

FIG. 13 is a sectional view taken along line 13-13 of FIG. 9 similar toFIG. 12;

FIG. 14 is an exploded top plan view of an alternate embodiment of thelens blank and auxiliary slab of the present invention;

FIG. 15 is a fragmented developed view similar to FIG. 9 depicting aplurality of blanks disposed about the periphery of a blocking wheel inaccordance with the alternate embodiment of the present invention; and,

FIG. 16 is a side sectional elevational view taken along the line 16-16of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly tothe drawings, it is first pointed out that unfinished workpieces to beblocked, ground and polished into semifinished multifocal lens blanksare preferably formed by molding or other means to a uniform size, shapeand thickness, and are formed of optical glass, plastic, or othersuitable material. The semifinished lens blank 10 produced in accordancewith the method of the present invention is depicted in phantom in FIG.3 and in more detail in FIGS. 5 through 7 and includes a first topsurface 12, upon which the desired fields of vision are ground prior toshipment to a prescription laboratory, and an under or concave surfaceupon which the final optical or ophthalmic prescription is ultimatelyground at the laboratory. The semifinished multifocal blank 12 depictedin FIG. 3 is bifocal and includes a distance field of vision l6 and anear field of vision 18 separated by the shoulder 20 which traverses theblank from one end to the other. The thickness of the distance portionbeing greater than that of the reading portion. It is to be understoodthat in its initial state, the convex surface 12 of the blank iscontinuous as represented by the solid lines of FIG. 3.

The blank 10 depicted in this preferred embodiment has a semiroundconfiguration in that the lower portion 22 of the blank 10 issubstantially semicircular in shape while that portion 24 opposite thelower portion 22 is substantially straight. This semiround configurationenables the blank to be processed by the prescription laboratory withoutany prior cribbing or cutting as would be required with the prior artsemifinished blank 26 depicted in FIG. 2, since the optical center ofthe blank of FIG. 3 corresponds to its geometric center and hence theproblems which give rise to the needs for cribbing are obviated.Further, the semiround shape results in a substantial saving in glasssince its volume is roughly percent less than that of a comparable priorart, rectangular blank. However, it should be noted that a considerableportion of that saving will be expended in the semifinishing operationas will be described. Since the peripheral configuration requires nofurther processing, the semiround blank possesses considerable marketingappeal because of the obvious time saving that it affords theprescription laboratory.

In one successful practice of this invention, optimum results occurredwhen the diameter of the semiround portion 22 was 58 mm. and the lengthof the straight portion 24 was 35 mm. The overall height of the blankwas 5 1.5 mm. with the distance portion being 29.0 mm. and the readingportion 22.5 mm. The spherical radius of curvature to the under orconcave surface was fixed at 88.33 mm. while the starting thickness andradius of the top surface varied with the nominal base curve power inaccordance with the following chart:

Spherical radius 4 Each of the above described blanks possesses aconstant 6.00

diopter underside curve for all bases and has a peripheral edge thatdoes not require any modification prior to surfacing by the prescriptionlaboratory. Further, the optical center of each blank is locatedessentially in the geometric center of blank thus eliminating andsubstantially reducing any tendency of the optical center to driftduring surface processing, thereby eliminating the need to preform theoutline of the lens blank prior to such surfacing.

It should be understood that the method of producing semifinished lensblanks in accordance with the present invention to be describedforthwith would apply equally to the production of blanks of any regularor irregular configuration.

The production of semifinished multifocal blanks from unfinishedworkpieces having the desired configuration requires that a plurality ofthe unfinished pieces be disposed about the outer circumferentialperiphery of a blocking wheel and affixed thereto. The radius of theblocking wheel must be such that the combination of the wheel radius andfinal thickness of the blank add up to the desired radius of the fieldof vision that is being ground. The grinding operation may be performedby bringing a grinding tool, such as a grinding Wheel, having a radiusof cross curvature equal to the spherical radius of the field of visionthat is sought to be imposed on the blank, in operative contact with theworkpiece while both the blocking wheel and grinding wheel rotate.

The prior art blocking wheel 28, which is depicted in FIG. 1 prior tothe grinding operation, readily displays that the straight sides 30 ofthe prior art blanks 26 were necessary to permit a side-by-sidesubstantially abutting relationship between adjacent blanks. Thisrelationship is necessary in order to provide the additional supportneeded by the processing tools to form relatively undistorted lenssurfaces and to prevent the tool from slipping off the operatingsurface.

In accordance with the present invention, an unfinished workpiece havingthe desired nonrectangular configuration of FIG. 3 may be transformedinto a lens blank by conventional grinding techniques. Referring to FIG.8, a plurality of unfinished partly round workpieces 10 are blockedabout the circumferential periphery of a blocking wheel 32 and affixedthereto by conventional adhesives such as epoxy, wax, lowmelting-pointalloy or pitch compounds known to the art or by mechanical clamping.Auxiliary slabs 34 are placed between adjacent blanks l0 and affixed tothe wheel by suitable means. The slabs may consist of solid pieces ofoptical glass or plastic but are not restricted to these materials andpractically any substance of suitable hardness will suffice. Thethickness of the slab 34 is substantially equal to the thickness of theblank 10 and the configuration of the slab 34 is such that it willminimize the gap between adjacent workpieces 10a and 10b so as toprovide the additional support needed by the surfacing tool 36 (depictedin phantom in FIGS. 12 and 13) and prevent the tool 36 from falling intothe gaps between adjacent workpieces, thereby permitting the processingto proceed. In this preferred embodiment, the workpiece 10 includes asemicircular lower portion 22, and the auxiliary slab 34 comprises asubstantially triangular member having concave adjacent sides 38 and 40.The radius of curvature of sides 38 and 40 is substantially equal to theradius of curvature of the circular lower portion 22 of the blank 10.The apex 42 formed at the juncture of sides 38 and 40 describes an anglewhich most conveniently fills the cusp formed by two adjacent pieces 10aand 10b and hence its size is determined by that of the blanks.

As seen in FIG. 9, workpieces and auxiliary slabs present asubstantially continuous surface about the circumferential periphery ofthe blocking wheel and thus enable the near and distant fields of visionto be ground and polished onto the blank without the danger of thegrinding tool falling between adjacent blanks or an aberrated surfaceforming resulting from the varying unit pressures exerted by thegrinding or polishing tool as the pattern of glass area under the toolchanges with the rotation of the blocking wheel.

An alternative embodiment of the present invention is depicted in FIGS.14 through 16. In this alternative embodiment, an auxiliary slab issecured to the workpiece prior to the blocking of the workpiece on thewheel. The combined configuration of the blank and slab then becomessuch as to permit a similar blank and slab combination to be brought insubstantial abutting relationship therewith when placed on the blockingwheel. Thus, for the semiround workpiece 44 depicted in FIG. 14, thealternative auxiliary slab 46 includes substantially straight sides 48and 50 and connected by the concave top 52. The curvature of the top 52is substantially similar to that of the lower portion 54 of theworkpiece 44. The slab is bonded to the workpiece by a conventionaladhesive such as epoxy, wax or a pitch compound or may be held in placeby mechanical clamping. The width of the slab, that is the dimensionbetween sides 48 and 50, should be such as to pennit a whole number ofcombined blanks and slabs to fill the entire circumferential peripheryof the blocking wheel 56 to which the blank is to be secured forprocessing. To insure the proper alignment of the workpiece and slab, soas to obtain the proper alignment of the workpiece with respect to thewheel 56, aligning lugs 58 and 60 are placed on the blank and slab,respectively. After the workpiece and slab are bonded together and theunit is secured to the blocking wheel along with a plurality of othersimilar units, the grinding procedure is carried on in a conventionalmanner and, when completed, the combined blank and slab are removed fromthe wheel and the slab is separated from the lens blank 62 so produced.

Thus, it can readily be appreciated by one skilled in the art that theabove-described method will enable the production of lens blanks havingany desired nonrectangular configuration.

It should be understood that modification may be made in the illustratedand described embodiments of my invention without departing from theinvention as set forth in the accompanying claims.

I claim:

1. in the method of making one-piece, multifocal lens blanks fromworkpieces having a convex side and a concave side wherein a grindingtool cooperates with a rotating blocking wheel to simultaneously grindthe desired field of vision on a multiplicity of substantially identicalworkpieces disposed about the peripheral surface of the rotatingblocking wheel, the major portion of the peripheral edge of theworkpieces being curved and the configuration of said workpieces beingsuch as to prevent the side-by-side placement of two such workpieces insubstantially abutting relationship along a major part of the adjacentportions of the curved peripheral edges of the adjacent workpieces onsaid wheel, comprising the steps of: providing a rotatable blockingwheel; mounting the workpieces and suitably shaped auxiliary slabs onthe peripheral surface of blocking wheel, the workpieces being arrangedin sideby-side relationship on the blocking wheel, the auxiliary slabsbeing interposed between adjacent workpieces so as to reduce any spacingbetween adjacent workpieces; and processing the convex sides of theworkpieces with a grinding tool employing the mounted slabs to preventaberrated surfaces from forming on said workpieces as a result ofvarying unit pressures exerted by the grinding tool as the pattern ofarea under the tool changes with a rotation the pattern the blockingwheel and to maintain the grinding tool on the workpiece and prevent thetool from falling into any space between adjacent workpieces.

2. The method in accordance with claim 1 wherein the peripheral edges oftwo adjacent workpieces define a gap and said auxiliary slabs aredisposed in the gap between adjacent workpieces, said auxiliary slabcomprising a substantially triangular member, one apex of saidtriangular member being disposed within the cusp formed between twoadjacent workpieces.

1. In the method of making one-piece, multifocal lens blanks from workpieces having a convex side and a concave side wherein a grinding tool cooperates with a rotating blocking wheel to simultaneously grind the desired field of vision on a multiplicity of substantially identical workpieces disposed about the peripheral surface of the rotating blocking wheel, the major portion of the peripheral edge of the workpieces being curved and the configuration of said workpieces being such as to prevent the side-by-side placement of two such workpieces in substantially abutting relationship along a major part of the adjacent portions of the curved peripheral edges of the adjacent workpieces on said wheel, comprising the steps of: providing a rotatable blocking wheel; mounting the workpieces and suitably shaped auxiliary slabs on the peripheral surface of blocking wheel, the workpieces being arranged in side-by-side relationship on the blocking wheel, the auxiliary slabs being interposed between adjacent workpieces so as to reduce any spacing between adjacent workpieces; and processing the convex sides of the workpieces with a grinding tool employing the mounted slabs to prevent aberrated surfaces from forming on said workpieces as a result of varying unit presSures exerted by the grinding tool as the pattern of area under the tool changes with a rotation the pattern the blocking wheel and to maintain the grinding tool on the workpiece and prevent the tool from falling into any space between adjacent workpieces.
 2. The method in accordance with claim 1 wherein the peripheral edges of two adjacent workpieces define a gap and said auxiliary slabs are disposed in the gap between adjacent workpieces, said auxiliary slab comprising a substantially triangular member, one apex of said triangular member being disposed within the cusp formed between two adjacent workpieces. 